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94 The Commercial Component site is located within a downtown urban setting, which is served by an existing storm drain system that outfalls into San Francisco Bay. The Commercial Component site is located within the Redwood Creek Watershed. As described in the Commercial Component Preliminary Engineering Report prepared by BKF Engineers (BKF) (BKF, “Preliminary Engineering Study, 901 El Camino Real, Redwood City, California 94063,” December 14, 2024), most on-site stormwater runoff flows overland to California Street and Winklebleck Street, where it is collected by drainage inlets that convey runoff to a 48” City storm drain line. This storm drain line drains into a creek and ultimately leaves the site through two 36” storm drain lines (p. 4). Stormwater continues to flow north before discharging into San Francisco Bay. The proposed site drainage pattern would match the existing drainage pattern to the extent possible. The Commercial Component proposes to relocate the existing on-site creek segment (i.e., Arroyo Ojo). A new 54” pipe would convey runoff from the relocated creek segment outlet into the existing storm drain system. Additionally, due to the vacation of the California Street right-of-way, an existing 12” storm drain pipe would be removed. In order to maintain the existing drainage pattern, the upstream runoff would be captured by a new system of 12” storm drain pipes and inlets along the proposed Franklin Street extension and would drain into the proposed 54” pipe system. Onsite runoff would first be collected by roof drains and conveyed to bioretention planters throughout the site. The Commercial Component would install bioretention planters located above and at ground level around the new building. Bioretention planters would be installed in sidewalk bulb-outs and the street frontages to treat runoff from the public right-of ways (ROW). Water would drain through curb ramps into the treatment planters and would then be conveyed into the storm drain system. The proposed Commercial Component would not contain uses that involve the discharge of cooled/heated water or pollutant-laden runoff. However, given the local urbanized area, the existing stormwater flows contain urban runoff with contaminants such as oil, grease, particulates, metals, and solvents. Because the proposed Commercial Component is subject to the requirements of a National Pollutant Discharge Elimination System (NPDES) permit for municipal stormwater runoff and other requirements of the City, County, and Regional Water Quality Control Board, the conditions of which limit the volume of contaminants allowed to enter the storm drain system, the proposed Commercial Component would not violate any water quality standards or waste discharge requirements. Furthermore, the DTPP program EIR (pp. 10-23 through 10-25) concluded that DTPP-facilitated development would not result in any significant water quality or stormwater drainage impacts. The proposed Commercial Component is in compliance with all applicable DTPP Standards relevant to hydrology and water quality and, as a result, water quality and stormwater drainage impacts would be less than significant. The City’s Drainage Guidelines for Commercial Development require post-development stormwater discharge to be equal to or less than pre-development discharge. The City mandates that proposed site conditions maintain the same runoff for the 30-year storm event as compared to the existing 10-year event. As discussed above, stormwater runoff collected on the Commercial Component site currently drains to the City stormwater system. Following treatment, per the City of Redwood City Stormwater Management and Discharge Control Program Ordinance (Redwood City Municipal Code Chapter 27A), stormwater from the Commercial Component would also continue to drain to the City stormwater system (BKF, p. 5). Commercial Component approval requires that stormwater control measures be designed and sized to treat runoff from the entire project site using flow- or volume-based sizing criteria, subject to review and approval by the City and consistent with the San Francisco Bay Region Municipal Regional Stormwater NPDES Permit (MRP) Provision C.3.d. The Preliminary Engineering Study included the Commercial Component’s drainage design and calculations in accordance with Redwood City Drainage Design Guidelines for Commercial Development and as required by DTPP Plan-Wide Amendments program SEIR Mitigation Measure UT-1d. The Commercial Component would incorporate traditional low impact development (LID) treatment measures in the onsite stormwater system design to meet Provision C.3 permit and San Mateo Countywide Stormwater Pollution Prevention Program (SMCSWPPP) requirements (BKF, p. 7). Stormwater from the subject site would be treated with a combination of raised and at-grade flow-through bioretention planters with impermeable liners and perforated underdrains. Each bioretention area is sized according to C.3 Technical Guidance. At-grade flow-through bioretention planters would also be installed on project frontages to treat runoff from El Camino Real, James Street, Winklebleck Street, and Franklin Avenue to meet the requirements of MRP 3.0. This component would manage stormwater runoff in 15 drainage management areas (DMA), which include a combination of onsite and offsite DMAs. Thirteen (13) of the 15 DMAs would treat runoff through a bioretention planter with underdrain, one DMA would treat runoff in a self-retaining landscape area, and the remaining DMA would treat runoff through a green roof system (BKF, Attachment 7 (C.3 Checklist)). ATTY/RESO.0028/CC RESO CEQA GUIDLINES (920 SHASTA) - EXHIBIT A REV: 04-22-25 VR Page 94 of 148